Electron discharge tube with trimming condenser



Nov. 22, 1949 J. A. B. ZAAT 2,488,791

ELECTRON DISCHARGE TUBE WITH TRIMMING CONDENSER Filed July 19, 1947 JOJLWIUJAZNOZDUSBEBMEDZLSM INVEN TOR.

BY%4%W AGEZVI.

Patented Nov. 22, 1949 ELECTRON DISCHARGE TUBE "TRIMMING CONDENSER Josephus Arnoldus'Bernardus 'Z'aat, Ein'd'hoven, Netherlands, v.assig'nor to Hartford National Bank and Trust Company, Hartford, Conn, as

trustee Application July 19, 1947, Serial No. 762,151 In the Netherlands August 6, 1946 2 Claims.

In the use of electron-discharge tubes it is generally of importance that each tube is adapted to be replaced by a tube of the same type without the necessity of altering the apparatus in which the tubes are used.

With the aid of modern methods, electron-dis charge tubes can be made in such manner, that substantially all vital characteristics of different specimens of a given type are uniform within very narrow limits. However, it has been found that in regard to capacities existing between the electrodes and with respect to surrounding component parts of the apparatus, the tolerated differences are so small that the manufacture of readily interchangeable tubes is practically impossible without incurring exceptionally high cost of production. This holds particularly for tubes for very high frequencies.

In prior Dutch patent application (No. 124,688) it has been proposed to avoid the aforesaid difficulty by providing a trimming condenser in a space which is bounded partly by the wall of the bulb, partly by shielding means of the tube. In this case a portion of the shielding means constitutes one electrode of the trimming condenser. In a given form of construction the other electrode may consist of a plate which is rigidly or rotatably fixed to a contact pin, a dielectric in the form of an insulating plate being provided between the electrodes of the trimming condenser. If the electrode is rigidly secured to the contact pin, the insulating plate is rotatably arranged and has such a shape that the quantity of dielectric material between the electrodes of the trimming condenser is changed upon displacement of the insulating plate.

In order that the various condenser parts engage each other at a sufficient pressure in an electron-discharge tube comprising a shielding plate and a trimming condenser of which one electrode is formed by a part of the shielding plate and is separated from the other electrode by a dielectric, the shielding plate is, according to the invention, provided with one or more incisions in a manner such that that portion of this plate, which functions as an electrode for the trimming condenser, engages the dielectric resiliently.

In order that the invention may be more clearly understood and readily carried into effect, it will now be described more fully with reference to the accompanying drawing, in which Fig. 1 shows an embodiment of a tube with trimming condenser according to the invention, in perspective, and Figs. 2 and 3 are views of the condenser in plan and section, respectively.

In the drawing the reference numeral l denotes the wall of the tube, 2 the shielding plate and 3 the contact pin which may be connected to an electrode which requires to be given a definite exact capacity.

Contact pin 3 is secured to a semi-circular metallisation 4 at the lower side of the bottom of the tube, this metallisation constituting an electrode of the trimming condenser. The metal shielding plate 2 constitutes the other electrode of this condenser. These two electrodes are separated by a dielectric in the form of an insulating plate 5 which is rotatable about pin 3 and exhibits an aperture 6 of such a shape that upon rotation of plate 5 the quantity of insulating material between the electrodes of the trimming condenser changes, with the result that the capacity of this condenser is changed. Rotation of plate 5 may be effected through the aperture 1. To prevent the shielding plate from being slightly pressed in upon introducing the tube into the tube holder, due to which the insulating plate might be shifted, the shielding plate is embossed at several points, thus forming elevations 10 with which the shielding plate rests on the bottom of the tube.

According to the invention incisions 8 and 9 are provided in the shielding plate 2, as a result of Which the portion functioning as an electrode of the trimming condenser, is resilient and engages the insulating plate 5 with a definite pressure. In this manner this plate cannot shift during transport and thermal strains in the shielding plate 2 cannot give rise to displacement of the plate.

Hereinbefore a definite form of construction has been described. It is obvious, however, that the incisions may exhibit different shapes and that, for instance, a plurality of electrodes of the tube may be trimmed in a manner according to the invention.

What I claim is:

1. An electric discharge tube having an envelope with a trimming condenser on the outside thereof for changing the capacity of the electrodes in said tube, said tube comprising a shielding plate, said plate having a portion forming one electrode of said condenser, a metal plate interposed between the said shielding plate and the said envelope forming the second electrode of said condenser, and a dielectric arranged between said condenser electrodes, said electrodeforming portion of the shielding plate having at least one incision for rendering said plate portion 4 having at least one incision for rendering said plate resilient, whereby said portion is yieldingly engaged with said insulating plate.

JOSEPHUS ARNOLDUS BERNARDUS ZAAT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Murphy Aug. 22, 1933 Number 

